Control system



Nov. 16, 1948. G. E. STOLTZ CONTROL SYSTEH Filed NOV. 2, 1946 IVNVENTORG/enn ESfO IZ 5W ATTO WITNESSES: if 1 n 7 7/ I vrnq Patented Nov. 16,1948 CONTROL SYSTEM Glenn E. Stoltz, Pittsburgh, Pa., asslgnor toWestlnghouse Electric Corporation, East Pittsburgh,

Pa., a corporation of Pennsylvania Application November 2, 1946, SerialNo. 707,477

9 Claims. 1

My invention relates, generally, to electrical control systems and ithas reierence, in particular, to control systems for tandem striprolling mills and the like.

Generally stated, it is an object of my invention to provide an improvedcontrol system for rolling mills and the like which is simple andinexpensive to manufacture, and which is reliable and efllcient inoperation.

More specifically, it is an object of my invention to provide forcontrolling the operation of the roll stand and reel motors of a tandemstrip rolling mill by means of regulating generators.

It is also an object of my invention to provide for using a regulatinggenerator, which is responsive to the speed and current of a motor, forcontrolling the energization of a magnetizing field winding on themotor.

Another object of my invention is to provide for regulating theoperation 01 a motor in accordance with predetermined characteristics ofthe motor load, and for additionally varying the energization of amagnetizing iield winding thereof in response to operation of speedcontrol means of the motor.

Yet another object of my invention is to provide for jointly varying thearmature voltage and field current of a motor to regulate the motortorque.

An important object of my invention is to provide for using a regulatinggenerator to maintain the energization of a magnetizing field winding onthe motor proportional to both the speed and load of the motor.

Yet another important object oi my invention is to provide forcontrolling the operation of a roll driving motor in a rolling mill bymeans of regulating generators which determine the energizations ofshunt and magnetizing field windings thereof and for varying theenergizations of these field windings in opposite senses.

A furher object of my invention is to provide for using a series orbooster generator to control the operation of a reel motor, and forvarying the voltage of said generator in accordance with theenergization oi the pattern. field winding of a regulating generatorasosciated with the preceding roll driving motor.

Other objects will, in part, be obvious and will, in part, be explainedhereinafter.

In practicing my invention in one of its forms. tensiometers are usedbetween any number of successive stands of a tandem strip rolling millto control the operation of the succeeding roll motor, although, in someinstances, it may be desirable to control the preceding motor. The

main field winding oi. the roll driving motor is energized by a mainregulating generator which is responsive to the operating position ofthe preceding tensiometer and to a predetermined pattern fieldenergization. A booster generator in series with the roll motor iscontrolled by a booster regulating generator which is responsive to theroll motor load. A magnetizing regulating generator responsive to thespeed and load of the roll motor maintains the magnetizing field windingexcitation in the proper relation to the motor speed by having itspattern field energizatlon varied in the oppositesense to variations inthe energization of the main field regulating generator. by using thetensiometer to vary the effective pattern field excitation of either orboth the main and booster regulating generators. A reel motor tensionregulator maintains the proper reel motor torque by maintaining apredetermined armature current through the medium of a bucking generatorwhich varies the reel motor armature voltage. The voltage of the buckinggenerator is varied in accordance with variations in the pattern fieldenergization of the regulating generators of the preceding stand.

For a more complete understanding of the nature and scope of myinvention, reference may be made to the following detailed descriptionwhich may be studied in connection with the accompanying drawing, inwhich the single figure is a diagrammatic view oi. a control system fora tandem strip rolling mill which embodies the invention in one of itsforms.

Referring to the drawing, the reference numeral in may denote,generally, a control system for a tandem strip rolling mill in which astrip of material l2 may be worked upon by roll stands l3 and I4 drivenby roll motors l5 and i6, respectively. For the purposes ofsimplification only one stand i4 controlled by tension responsive meansI! is shown. Any number of such stands may, of course, be used. Thestrip may be wound on a reel l8 driven by a reel motor 20.

The roll motor l5 may be provided with an armature 22, a main or shuntfield winding 23, and a magnetizing field winding 24. The armature 22may be connected to a suitable source of electrical energy representedby the conductors 26 and 21, which may be connected to a source ofvariable voltage. The main shunt field winding 23 may be energized froma main regu-.

lating generator 28 having an armature 29, a

Tension between stands is maintained 3 self-energizing or series fieldwinding 36, a pattern field, winding 3|, a differential field winding32, and an auxiliary pattern or bias field winding 33.

The pattern and bias field windings 3| and 33 may be connected to asuitable source of electrical energy, such as the control bus 35 throughrheostats 35 and 31, respectively, for basically determining theenergization of the main field winding 23 of the roll motor I5. Thedifferential field winding 32 may be connected in series circuitrelation with the main field winding 23 for opposing the pattern andbias field windings so as to obtain a balance when the field current ofthe main field winding 23 is of the correct value. The self-enegrizingfield winding 30 is also connected in series circuit relation with themain field winding 23 and is arranged to maintain the output voltage ofthe regulator generator 28 at the necessary value to maintain a propervalue of field current under balanced conditions.

In order to regulate the speed of the roll motor I and compensate forthe demagnetizing effects of the armature current under different loadconditions, energization of its magnetizing field winding 24 may beeffected by means of a magnetizing regulating generator 40. Thegenerator 40 may be provided with an armature 4i, a pattern fieldwinding 42, a self-energizing field winding 43, and a differential fieldwinding 44. The self-energizing and differential field windings 43 and44 may be connected in series circuit relation with the magnetizingfield winding 24 of the motor I5, while the pattern field winding 42 maybe energized from a pilot generator 45. The pilot generator may bedriven by the roll motor I5 and its field winding 46 may be energized inaccordance with the load of the roll motor by being connected across ashunt 41 in the armature circuit thereof, so that its output isresponsive to both the speed and load of the motor I5.

Control means, such as the rheostat 48, may be provided for varying theenergizati-on of the pattern field windings 42. Since the demagnetizingeffect of the armature current varies inversely with the speed of themotor, the rheostat 48 may be operatively connected to the rheostat 36which determines the energization of the main field winding 23, so as toeffect joint operation of the rheostats in opposite senses, unless itis;desired to use the magnetizing field winding 24 for producing aseries or drooping load characteristic in which case the rheostats mayoperate in the same SBDSBS.

In order to provide for maintaining or regulating the speed of the rollmotor l5 under varying load conditions, a booster generator 50 may beutilized to vary the voltage applied to the armature 22 of the rollmotor l5 primarily to compensate for the IR drop in the roll motorarmature circuit. The booster generator 50 may be provided with a fieldwinding 5| which may be energized from a booster regulating generator52. The regulating generator 52 and booster generator 50 may be drivenby a common motor 53. The output of the booster regulating generator 52may be controlled by providing it with a pattern field winding 54, whichmay be energized in accordance with the roll motor armature current. Thewinding 54 may, for example, be connected across a shunt 55 in circuitwith the armatures of the booster generator 50 and the roll motor l5. Anauxiliary pattern or bias field winding 51 on 4 the regulating generator52 may be energized from the conductors 35 through a rheostat 59. Adiiferential field winding 59 may be connected across the armature ofthe booster generator 59 for producing a field balancing the pattern andbias fields to regulate the output voltage thereof.

The roll motor I6 may be provided with an armature 60, a main or shuntfield winding 6|, and a magnetizing field winding 62. The armature 60may be connected to the variable voltage source represented byconductors 26 and 21. The main field winding 6| may be energized from amain regulating generator 64 similar to the regulating generator 29 ofthe roll motor IS. The regulating generator 64 may be provided with aself-energizing field winding 65 and a differential field winding 66connected in series circuit relation with the main field winding 6|.This regulating generator also may-be provided with a pattern fieldwinding 81 connected to the conductors 35 through a suitable rheostat68, and a control or bias field winding 69 the purpose of which will beexplained hereinafter.

Energization of the magnetizing field winding 62 of the roll motor I6may be effected by connecting it to a magnetizing regulating generatorI0, which may be provided with self-energizing and differential fieldwindings II and 12 connected in series circuit relation with themagnetizing field winding 62 and a pattern field winding I3 which may beenergized from a pilot generator 14 through a suitable rheostat I5. Thefield winding I6 of the pilot generator may be energized in accordancewith the armature current ofthe roll motor I6 by connecting it acrossthe shunt II in the armature circuit thereof.

Normal regulation of the roll motor I6 may be effected by varying thevoltage applied to its armature by means of a booster generator having afield winding 8|. Energization of the field winding 8i may be effectedfrom a booster regulating generator 82 having a self-energizing fieldwinding 89 connected in circuit relation with the field winding 8|, acontrol or bias field winding 84, a differential field winding 85connected across the armature of the booster generator, and a patternfield winding 86 which may be connected across a shunt 91 in thearmature circuit of the motor I6.

In order to provide for controlling the tension in the strip I2, tensionresponsive means, such as the tensiometer II, may be provided embodyinga bell crank 9| which may be actuated in accordance with the tension inthe strip I2 against the action of an operating spring or other sourceof elastic force. The operating position of the bell crank 9i will,therefore, depend on the tension in the strip I2.

Movement of the bell crank 9i may be transmitted by means of asynchro-tie system 92 to actuate suitable regulating devices, such asthe rheostatic regulators 93 and 94. The rheostatic devices 93 and 94may comprise, for example, a plurality of flexible contact fingers 96which may be progressively actuated into the contact with each other bymeans of arms 91 operated by cams 98 actuated by the synchro-tie system92. The flexible contact fingers 96 may be connected to resistors I00and IIII at spaced intervals for varying the effective values thereof.By connecting the resistors I00 and IOI in circuit relation with thecontrol windings 69 and 84 of the main and magnetizing regulatinggenerators 64 and 82, respectively, the respective outputs of thesegenerators may be varied to reduce or increase the speed of the rollmotor I0 and reduce or increase the tension of the strip t2 between thestands I3 and II. The tensiometer I1 may be used either to regulate thetension during normal running when working at high speeds withlightstrip, or it may be adjusted to be effective only when the tensionincreases to about 50% above normal, in the case or heavy strip at lowspeeds. Y

The reel motor 20 may be provided with an armature I03 and a fieldwinding I04. The field winding I04 may be connected. to a suitablesource of electrical energy, such as the conductors 35, through acontrol resistor I05. The armature I03 may be connected to the variablevoltage bus conductors 2B and I! so that the speed of the reel motorwill vary substantially in proportion the field winding 8| willdecrease. Both results tend to slow down the roll motor I6 and reducethe tension to the predetermined desired value. When the roll motor I 6is operating at base speed, the change in the voltage of the boostergener ator 80 will predominate, while both the change in theenergization of the main field winding 0| and the change in theenergization of the magnetizing field winding 62 will be efiective whenthe motor is operating above the base speed, where the effects are morecritical.

Should the rheostat 68 be adjusted to increase the speed or the rollmotor I6 by reducing the to variations in the speed of the roll motorsas determined by variation oi the voltage between the conductors 2B and21. The tension in the strip I2 between the roll stand I 4. and the reelI8 may be determined by regulating the voltage applied to the armatureI03 of the reel motor through the use of a bucking or boosting generatorI01 having an auxiliary field winding I08 and a main field winding I 09.

The auxiliary field winding I08 may be energized from a tensionregulating generator IIO having, a self-energizing field winding IIIconnected in series circuit relation with the field winding I08, apattern field winding III, a bias field winding H3, and a differentialfield winding 4.. The differential field winding may be energized inaccordance with the reel motor armature current by connecting it acrossa shunt HE. A rheostat i I8 may be provided for adjusting theenergization of the pattern field winding II2 to determine the value ofthe tension in the strip I2. Suitable means represented by the rheostatII'I may be provided, if desired, for varying the effective value of thebias field winding energiza= tion during accelerating and deceleratingto compensate for the inertia of the strip reel and other rotatingparts.

In the operation of the system, the voltages produced by the boostergenerators 50 and 80 will be proportional-to the loads on the rollmotors I5 and I8, respectively, so they compensate for the ohmic dropsin the armature circuits of these motors. The voltages produced by themagnetizing regulating generators 40 and 70 are respectivelyproportional to the loads and speeds of these motors also. As a resultthese roll motors I5 and I6 respond, regardless of the particular loador the value of torque required to accelerate or retard the mill, asthough they are operating under no load conditions. Accordingly,accurate synchronization of these motors is readily obtained under allconditions.

When the roll motors i5 and I8 are operating at base speed, the mainfield winding circuit is essentially saturated and the principalregulation will be obtained through armature control by the boostergenerators 50 and 80. Any variation in strip tension above apredetermined value is immediately reflected in the position of thebellcrank SE of the tensiometer device I! which alters the effectivevalues of the resistors I00 and IOI. The energization of the controlfield windings 89 and 81 of both the main and booster regulatinggenerators 64 and 02, respectively, are altered correspondingly. Theenergization of the main field winding GI 01 the roll motor IE will thusbe increased should the tension of the strip I2. increase while theenergization of energization of the pattern field winding 61, therheostat I5 will be concurrently adjusted to increase the energizationof the pattern field winding I3 so as to provide greater compensationfor the increased demagnetizing effect of the armature current at higherspeeds. At the same time, the field rheostat I20 of the auxiliary fieldwinding I09 of the reel booster generator III? will also be actuated toincrease the voltage applied to the armature E03 of the reel motor 20 soas to maintain the predetermined tension in the strip I2.

From the above description and the accompanying drawing, it will beapparent that I have provided a tandem strip mill control system whichis simple and eflective in design and which is reliable and efficient inoperation. Regulation of the tension of the strip is readily effectedunder all operating conditions so that strip may be rolled at relativelyhigh tension without fear of breakage. By compensating for themagnetizing effect and for the ohmic drops in the system closeregulation and accurate gauging .of the material may be obtained over awide range of speeds.

This feature is particularly valuable due to the fact that the tensionbetween the roll stands on the delivery and of the strip mill increasesas the mill speed is decreased from normal running speed to a threadingspeed of possibly t, normal running or operating speed. With the controlas described, tension is maintained and accurate gauge obtained undernormal running conditions. When the mill is slowed down, this controlwill attempt to maintain gauge up to a predetermined value of tensionwhich can be sustained without too much risk of breaking the strip, Atthis I value. either the voltage on the roll motor armature or on itsmain field winding, or both, are biased to reduce the speed of the rollmotor suiflcient to prevent the tension from increasing beyond itspredetermined limit.

The voltage on the booster generator may not only be reduced to zerovalue, but increased in the opposite direction to still further reducethe voltage on the roll motor.

Another feature which may be incorporated in the magnetizing generatorcontrol is to increase its efiect to provide suilicient series fieldto'cause a slight droop in speed of the roll motor with increase inarmature load current. This can be done to assure stable operation ofthe motor under all load and speed conditions. When ing drawings shallhe considered as illustrative and not in a limiting sense.

I claim as my invention:

1. A control system for a motor having an armature and a field windingcomprising, circuit means connecting the armature to a source ofelectrical energy, control means responsive to the speed of the motorand a load on the motor, and a regulating generator connected toenergize the field winding of the motor, said regulating generator beingdifferentially responsive to said means and to the. field current of themotor.

2. In a control system for a motor having an armature and field winding,circuit means connecting the armature to a source of electrical energy,control means connected in circuit with the motor armature and thesource operable to vary the voltage applied to the armature, controlmeans jointly responsive to the speed of the rno= tor and to a load onthe motor, and regulating means responsive to said means operable tovary the output of the control means and energization of said fieldwinding.

3. In a control system for a roll driving motor of a strip rolling millhaving an armature and i a field winding, means producing a voltage re=sponsive to the tension of the strip, a regulating geneartordifferentially responsive to said voltage and to the current oi one ofthe field windings connected to maintain the energization or said fieldwinding, circuit means connecting the ar= mature of the roll motor to asource of electrical energy, control means connected in circuit relatlonwith said armature to vary the voltage applied thereto from the source,and regulating means responsive to the first mentioned means operable tocontrol operation of said means.

i. In a control system for a motor having an armature and a fieldwinding, control means pro= ducing a voltage proportional to the speedand load of the motor, and a regulating generator connected to energizesaid field winding-differentially with respect to said voltage and thefield winding current.

5. In a control system for a strip mill motor having an armature and aplurality of field wind ings, circuit means connecting the armature to asource of electrical energy, control means op= erable to produce acontrol voltage proportional to the speed and the load of the motor, aregulating generator connected to energize one or the field windingsdiilerentially with respect to said control voltage and the current inthe field winding, an additional regulating generator con= nected toenergize another of the field windings in accordance with the tension ofthe strip, and means operable to vary the energizations of the fieldwindings Jointly.

6. For use with a strip mill motor having an armature and a plurality ofiield windings, means producing a voltage proportional to the speed andthe load of the mill motor, a regulating gener= ator connected toenergize one of said field winchings in accordance with a predeterminedload characteristic of the motor, a pilot generator op= erablc toproduce a voltage having predetermined relations to the speed and loadof the motor, a regulating generator connected to energize another oneor said field windings in accordance with the voltage of said pilotgenerator, and means jointly varying the energizations of said fieldwindings in opposite senses.

l. in a control system for a strip mill motor having an armatureconnected to a source of electrical energy and a plurality of fieldwindings, means producing a variable voltage responsive to the tensionoi a strip of material in the mill, a regulating generator of thesell-energizing type connected to energize one of the field windings inpredetermined relation to the variable voltage of the tension device, apilot generator driven hy the motor and having it held winding energizedin accordance with the armature current of the motor for producing avariable control voltage, an additional regulating generator of thesellenergizing type connected to energize another oi the field windingsin predetermined relation to said variable control voltage, and meansoper= able to vary the predetermined relations oi the energizations ofsaid field windings in opposite senses jointly.

8. For use with a roll stand adapted to worir on strip material, a motorconnected to drive said roll stand, means responsive to the tension oithe strip operable to maintain the speed of the motor in predeterminedrelation to the strip tension, control means responsive to the speed andload or the motor to produce a predetermined counterdemagnetizing eflectin the motor, a reel motor operablein predetermined relation with theroll motor to wind the strip, and means jointly operable to vary saidpredetermined relations.

ii. in a control system for a roll driving motor having an armaturearranged to be energized from a source of electrical energy and aplurality of field windings; a pilot generator driven by the roll motorfor producing a variable control vo1tage and having a field windingenergized in ac cordance with the armature current of the roll motor; aregulating generator connected to encr gize one of the motor fieldwindings and having a pattern field winding energized in accordance withsaid variable control voltage and a difi'erential field windingenergized in accordance with the armature current oi the roll motor; anadditional regulating generator connected to energize another of themotor field windings, said generator having a pattern field windingenergized irom a source of substantially constant control voltage, acumulative control field winding energized in accordance with thetension of the strip and a difierential ileld winding energized inaccordance with the current 01 said another field winding; and meansoperable to vary the energizations of the pattern field windings jointlyin opposite senses.

GLENN E. QTULTZ.

No references cited.

